Techniques for promoting current efficiency in electrochemical separation systems and methods

ABSTRACT

An electrochemical separation system may be modular and may include at least a first modular unit and a second modular unit. Each modular unit may include a cell stack and a frame. The frame may include a manifold system. A flow distribution system in the frame may enhance current efficiency. Spacers positioned between modular units may also enhance current efficiency of the system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application Ser. No. 61/413,021, filed on Nov. 12,2010, titled “CROSS-FLOW ELECTROCHEMICAL DEIONIZATION DEVICE AND METHODSOF MANUFACTURING THEREOF” and to U.S. Provisional Patent ApplicationSer. No. 61/510,157, filed on Jul. 21, 2011, titled “MODULAR CROSS-FLOWELECTRODIALYSIS DEVICES AND METHODS OF MANUFACTURING THEREOF,” theentire disclosure of each of which is hereby incorporated herein byreference in its entirety for all purposes.

FIELD OF THE DISCLOSURE

Aspects relate generally to electrochemical separation and, moreparticularly, to modular electrochemical systems and methods.

SUMMARY

In accordance with one or more aspects, an electrochemical separationsystem may comprise a first electrode, a second electrode, a firstelectrochemical separation modular unit having a first cell stackdefining a plurality of alternating depleting compartments andconcentrating compartments supported by a first frame, the firstelectrochemical separation modular unit positioned between the firstelectrode and the second electrode, and a second electrochemicalseparation modular unit, adjacent to and in cooperation with the firstelectrochemical separation modular unit, having a second cell stackdefining a plurality of alternating depleting compartments andconcentrating compartments supported by a second frame, the secondelectrochemical separation modular unit positioned between the firstelectrochemical separation modular unit and the second electrode.

In accordance with one or more aspects, a method of assembling anelectrochemical separation system may comprise mounting a firstelectrochemical separation modular unit having a first cell stacksurrounded by a first frame in a vessel between a first electrode and asecond electrode, and mounting a second electrochemical separationmodular unit having a second cell stack surrounded by a second frame inthe vessel between the first electrochemical separation modular unit andthe second electrode.

In accordance with one or more aspects, an electrochemical separationmodular unit may comprise a cell stack defining a plurality ofalternating depleting compartments and concentrating compartments, and aframe surrounding the cell stack and including a manifold systemconfigured to facilitate fluid flow through the cell stack.

In accordance with one or more aspects, a flow distributor forelectrochemical separation may comprise a plurality of first passagesoriented in a first direction and configured to deliver feed to at leastone compartment of an electrochemical separation device, and a pluralityof second passages oriented in a second direction, the plurality ofsecond passages in fluid communication with the plurality of firstpassages and with an inlet manifold associated with the electrochemicalseparation device.

In accordance with one or more aspects, an electrochemical separationsystem may comprise a first electrode, a second electrode, a firstelectrochemical separation modular unit including a plurality ofalternating depleting compartments and concentrating compartmentspositioned between the first and second electrodes, a secondelectrochemical separation modular unit including a plurality ofalternating depleting compartments and concentrating compartments, thesecond electrochemical separation modular unit arranged in cooperationwith the first electrochemical separation modular unit and positionedbetween the first electrochemical separation modular unit and the secondelectrode, and a spacer disposed between and adjacent the first andsecond electrochemical separation modular units configured to reducecurrent loss within the system.

Still other aspects, embodiments, and advantages of these exemplaryaspects and embodiments, are discussed in detail below. Embodimentsdisclosed herein may be combined with other embodiments in any mannerconsistent with at least one of the principles disclosed herein, andreferences to “an embodiment,” “some embodiments,” “an alternateembodiment,” “various embodiments,” “one embodiment” or the like are notnecessarily mutually exclusive and are intended to indicate that aparticular feature, structure, or characteristic described may beincluded in at least one embodiment. The appearances of such termsherein are not necessarily all referring to the same embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one embodiment are discussed below withreference to the accompanying figures, which are not intended to bedrawn to scale. The figures are included to provide illustration and afurther understanding of the various aspects and embodiments, and areincorporated in and constitute a part of this specification, but are notintended as a definition of the limits of the invention. Where technicalfeatures in the figures, detailed description or any claim are followedby references signs, the reference signs have been included for the solepurpose of increasing the intelligibility of the figures anddescription. In the figures, each identical or nearly identicalcomponent that is illustrated in various figures is represented by alike numeral. For purposes of clarity, not every component may belabeled in every figure. In the figures:

FIG. 1 is a schematic illustration of a stack of cell pairs in a frameof unitary construction in accordance with one or more embodiments;

FIG. 2 is a schematic illustration of Section A-A in FIG. 1 inaccordance with one or more embodiments;

FIG. 3 is a schematic illustration of showing dilute flow from slots toan inlet of dilute flow compartments in accordance with one or moreembodiments;

FIG. 4 is a schematic illustration of a method for potting corners withadhesive in accordance with one or more embodiments;

FIG. 5 is a schematic illustration of stack in a frame with inlet andoutlet ports oriented vertically in accordance with one or moreembodiments;

FIG. 6 is a schematic illustration of a flow path in accordance with oneor more embodiments;

FIG. 7 is a schematic illustration of potential current bypass throughslots in accordance with one or more embodiments;

FIG. 8 is a schematic illustration horizontal blocks to reduce currentbypass in accordance with one or more embodiments;

FIG. 9 is a schematic illustration of staggered horizontal blocks inaccordance with one or more embodiments;

FIG. 10 is a schematic illustration of a frame with separatelyfabricated grid in accordance with one or more embodiments;

FIG. 11 is a schematic illustration of grids with staggered blocks inaccordance with one or more embodiments;

FIG. 12 is a schematic illustration of a frame assembled from foursections in accordance with one or more embodiments;

FIG. 13 is a schematic illustration of an electrochemical separationsystem in accordance with one or more embodiments;

FIG. 14 is a schematic illustration of a modular unit with a stackinserted and potted into a frame in accordance with one or moreembodiments;

FIG. 15 is a schematic illustration of a view through Section A-A inFIG. 14 in accordance with one or more embodiments;

FIG. 16 is a schematic illustration showing details of FIG. 15 inaccordance with one or more embodiments;

FIG. 17 is a schematic illustration of a view through Section B-B inFIG. 14 in accordance with one or more embodiments;

FIG. 18 is a schematic illustration of a section through a modular unitin accordance with one or more embodiments;

FIG. 19 is a schematic illustration of an exploded view of an ED devicein accordance with one or more embodiments;

FIG. 20 is a schematic illustration of a view through Section A-A inModular Unit 1 of FIG. 19 in accordance with one or more embodiments;

FIG. 21 is a schematic illustration of a view through Section B-B inModular Unit 2 of FIG. 19 in accordance with one or more embodiments;

FIG. 22 is a schematic illustration of an arrangement of membranes andcells in an ED device in accordance with one or more embodiments;

FIG. 23 is a schematic illustration of a section view through anassembled ED device in accordance with one or more embodiments;

FIG. 24 is a schematic illustration of a detailed view of FIG. 23 inaccordance with one or more embodiments;

FIG. 25 is a schematic illustration of a frame with cylindrical outershape in accordance with one or more embodiments;

FIG. 26 is a schematic illustration of an ED device in a cylindricalvessel with molded endplates in accordance with one or more embodiments;

FIG. 27 is a schematic illustration of a prototype modular unit in aclear acrylic cylinder in accordance with one or more embodiments;

FIG. 28 is a schematic illustration of flow through a stack of cellpairs in accordance with one or more embodiments;

FIG. 29 is a schematic illustration of a cell stack in a frame withslots in accordance with one or more embodiments;

FIG. 30 is a schematic illustration of flow through a frame and stack ofcell pairs in accordance with one or more embodiments;

FIG. 31 is a schematic illustration of transport processes in apreferred ED modular unit in accordance with one or more embodiments;

FIG. 32 is a schematic illustration of transport processes in an EDmodular unit with current inefficiencies in accordance with one or moreembodiments;

FIG. 33 is a schematic illustration of transport processes in an EDmodular unit with current inefficiencies and water loss in accordancewith one or more embodiments;

FIG. 34 is a schematic illustration of current paths in a modular unitin accordance with one or more embodiments;

FIG. 35 is a schematic illustration of fluid volume in flow passagesinside a modular unit frame in accordance with one or more embodiments;

FIG. 36 is a schematic illustration of inlet flow passages in accordancewith one or more embodiments;

FIG. 37 is a schematic illustration of examples of paths for currentbypass around the stack in accordance with one or more embodiments;

FIG. 38 is a schematic illustration of staggered vertical passages inaccordance with one or more embodiments;

FIG. 39 is a schematic illustration of vertical slots and horizontalgrooves in an insert in accordance with one or more embodiments;

FIG. 40 is a schematic illustration of a frame with recesses for insertsin accordance with one or more embodiments;

FIG. 41 is a schematic illustration of a frame with an insert to beinstalled in accordance with one or more embodiments;

FIG. 42 is a schematic illustration of a section view showing flow pathsin an assembled modular unit in accordance with one or more embodiments;

FIG. 43 is a schematic illustration of a molded frame in accordance withone or more embodiments;

FIG. 44 is a schematic illustration of a molded frame with circularperiphery in accordance with one or more embodiments;

FIG. 45 is a schematic illustration of an insert with horizontal grooveson a curved side in accordance with one or more embodiments;

FIG. 46 is a schematic illustration of a molded frame with horizontalgrooves in recesses for inserts in accordance with one or moreembodiments;

FIGS. 47A-47C present schematic illustrations of a modular unitincluding extended end membranes in accordance with one or moreembodiments;

FIG. 48 presents a schematic illustration of modular units connectedwith flanges in accordance with one or more embodiments;

FIG. 49 presents a schematic illustration of a manifold associated withan insert in accordance with one or more embodiments; and

FIG. 50 presents data referenced in an accompanying Example inaccordance with one or more embodiments.

DETAILED DESCRIPTION

In accordance with one or more embodiments, a modular electrochemicalseparation system, which may also be referred to as an electricalpurification device or apparatus, may enhance the efficiency and overallflexibility of various treatment processes. In some embodiments,cross-flow electrochemical separation devices, such as cross-flowelectrodialysis (ED) devices, may be implemented as an attractivealternative to traditional plate-and-frame devices. In some embodiments,current inefficiencies in cross-flow electrochemical separation devicesmay be reduced. In at least certain embodiments, current inefficiencydue to current bypass through inlet and outlet manifolds may beaddressed. Energy consumption and membrane requirements may also bereduced, both of which may affect life cycle cost in variousapplications. In some embodiments, at least 85% membrane utilization maybe achieved. Reduction in membrane requirement may in turn result inreduction in manufacturing cost, weight and space requirements forelectrochemical separation devices. In some specific embodiments, theprocess efficiency of cross-flow ED devices may be significantlyimproved. In some embodiments, the efficiency of electrochemicalseparation systems may be improved for desalination of brackish water,seawater and brines from oil and gas production. In at least someembodiments, the cost competitiveness of ED may be improved incomparison to RO which is currently the dominant technology fordesalination.

Devices for purifying fluids using electrical fields are commonly usedto treat water and other liquids containing dissolved ionic species. Twotypes of devices that treat water in this way are electrodeionizationand electrodialysis devices. Within these devices are concentrating anddiluting compartments separated by ion-selective membranes. Anelectrodialysis device typically includes alternating electroactivesemipermeable anion and cation exchange membranes. Spaces between themembranes are configured to create liquid flow compartments with inletsand outlets. An applied electric field imposed via electrodes causesdissolved ions, attracted to their respective counter-electrodes, tomigrate through the anion and cation exchange membranes. This generallyresults in the liquid of the diluting compartment being depleted ofions, and the liquid in the concentrating compartment being enrichedwith the transferred ions.

Electrodeionization (EDI) is a process that removes, or at leastreduces, one or more ionized or ionizable species from water usingelectrically active media and an electric potential to influence iontransport. The electrically active media typically serves to alternatelycollect and discharge ionic and/or ionizable species and, in some cases,to facilitate the transport of ions, which may be continuously, by ionicor electronic substitution mechanisms. EDI devices can compriseelectrochemically active media of permanent or temporary charge, and maybe operated batch-wise, intermittently, continuously, and/or even inreversing polarity modes. EDI devices may be operated to promote one ormore electrochemical reactions specifically designed to achieve orenhance performance. Further, such electrochemical devices may compriseelectrically active membranes, such as semi-permeable or selectivelypermeable ion exchange or bipolar membranes. Continuouselectrodeionization (CEDI) devices are EDI devices known to thoseskilled in the art that operate in a manner in which water purificationcan proceed continuously, while ion exchange material is continuouslyrecharged. CEDI techniques can include processes such as continuousdeionization, filled cell electrodialysis, or electrodiaresis. Undercontrolled voltage and salinity conditions, in CEDI systems, watermolecules can be split to generate hydrogen or hydronium ions or speciesand hydroxide or hydroxyl ions or species that can regenerate ionexchange media in the device and thus facilitate the release of thetrapped species therefrom. In this manner, a water stream to be treatedcan be continuously purified without requiring chemical recharging ofion exchange resin.

Electrodialysis (ED) devices operate on a similar principle as CEDI,except that ED devices typically do not contain electroactive mediabetween the membranes. Because of the lack of electroactive media, theoperation of ED may be hindered on feed waters of low salinity becauseof elevated electrical resistance. Also, because the operation of ED onhigh salinity feed waters can result in elevated electrical currentconsumption, ED apparatus have heretofore been most effectively used onsource waters of intermediate salinity. In ED based systems, becausethere is no electroactive media, splitting water is inefficient andoperating in such a regime is generally avoided.

In CEDI and ED devices, a plurality of adjacent cells or compartmentsare typically separated by selectively permeable membranes that allowthe passage of either positively or negatively charged species, buttypically not both. Dilution or depletion compartments are typicallyinterspaced with concentrating or concentration compartments in suchdevices. In some embodiments, a cell pair may refer to a pair ofadjacent concentrating and diluting compartments. As water flows throughthe depletion compartments, ionic and other charged species aretypically drawn into concentrating compartments under the influence ofan electric field, such as a DC field. Positively charged species aredrawn toward a cathode, typically located at one end of a stack ofmultiple depletion and concentration compartments, and negativelycharged species are likewise drawn toward an anode of such devices,typically located at the opposite end of the stack of compartments. Theelectrodes are typically housed in electrolyte compartments that areusually partially isolated from fluid communication with the depletionand/or concentration compartments. Once in a concentration compartment,charged species are typically trapped by a barrier of selectivelypermeable membrane at least partially defining the concentrationcompartment. For example, anions are typically prevented from migratingfurther toward the cathode, out of the concentration compartment, by acation selective membrane. Once captured in the concentratingcompartment, trapped charged species can be removed in a concentratestream.

In CEDI and ED devices, the DC field is typically applied to the cellsfrom a source of voltage and electric current applied to the electrodes(anode or positive electrode, and cathode or negative electrode). Thevoltage and current source (collectively “power supply”) can be itselfpowered by a variety of means such as an AC power source, or forexample, a power source derived from solar, wind, or wave power. At theelectrode/liquid interfaces, electrochemical half cell reactions occurthat initiate and/or facilitate the transfer of ions through themembranes and compartments. The specific electrochemical reactions thatoccur at the electrode/interfaces can be controlled to some extent bythe concentration of salts in the specialized compartments that housethe electrode assemblies. For example, a feed to the anode electrolytecompartments that is high in sodium chloride will tend to generatechlorine gas and hydrogen ion, while such a feed to the cathodeelectrolyte compartment will tend to generate hydrogen gas and hydroxideion. Generally, the hydrogen ion generated at the anode compartment willassociate with a free anion, such as chloride ion, to preserve chargeneutrality and create hydrochloric acid solution, and analogously, thehydroxide ion generated at the cathode compartment will associate with afree cation, such as sodium, to preserve charge neutrality and createsodium hydroxide solution. The reaction products of the electrodecompartments, such as generated chlorine gas and sodium hydroxide, canbe utilized in the process as needed for disinfection purposes, formembrane cleaning and defouling purposes, and for pH adjustmentpurposes.

Plate-and-frame and spiral wound designs have been used for varioustypes of electrochemical deionization devices including but not limitedto electrodialysis (ED) and electrodeionization (EDI) devices.Commercially available ED devices are typically of plate-and-framedesign, while EDI devices are available in both plate and frame andspiral configurations.

One or more embodiments relate to devices that may purify fluidselectrically that may be contained within a housing, as well as methodsof manufacture and use thereof. Liquids or other fluids to be purifiedenter the purification device and, under the influence of an electricfield, are treated to produce an ion-depleted liquid. Species from theentering liquids are collected to produce an ion-concentrated liquid.

In accordance with one or more embodiments, an electrochemicalseparation system or device may be modular. Each modular unit maygenerally function as a sub-block of an overall electrochemicalseparation system. A modular unit may include any desired number of cellpairs. In some embodiments, the number of cell pairs per modular unitmay depend on the total number of cell pairs and passes in theseparation device. It may also depend on the number of cell pairs thatcan be thermally bonded and potted in a frame with an acceptable failurerate when tested for cross-leaks and other performance criteria. Thenumber can be based on statistical analysis of the manufacturing processand can be increased as process controls improve. In some non-limitingembodiments, a modular unit may include about 50 cell pairs. Modularunits may be individually assembled and quality control tested, such asfor leakage, separation performance and pressure drop prior to beingincorporated into a larger system. In some embodiments, a cell stack maybe mounted in a frame as a modular unit that can be testedindependently. A plurality of modular units can then be assembledtogether to provide an overall intended number of cell pairs in anelectrochemical separation device. In some embodiments, an assemblymethod may generally involve placing a first modular unit on a secondmodular unit, placing a third modular unit on the first and secondmodular units, and repeating to obtain a plurality of modular units of adesired number. In some embodiments, the assembly or individual modularunits may be inserted into a pressure vessel for operation. Multi-passflow configurations may be possible with the placement of blockingmembranes and/or spacers between modular units or within modular units.A modular approach may improve manufacturability in terms of time andcost savings. Modularity may also facilitate system maintenance byallowing for the diagnosis, isolation, removal and replacement ofindividual modular units. Individual modular units may includemanifolding and flow distribution systems to facilitate anelectrochemical separation process. Individual modular units may be influid communication with one another, as well as with centralmanifolding and other systems associated with an overall electrochemicalseparation process.

In accordance with one or more embodiments, the efficiency ofelectrochemical separation systems may be improved. Current loss is onepotential source of inefficiency. In some embodiments, such as thoseinvolving a cross-flow design, the potential for current leakage may beaddressed. Current efficiency may be defined as the percentage ofcurrent that is effective in moving ions out of the dilute stream intothe concentrate stream. Various sources of current inefficiency mayexist in an electrochemical separation system. One potential source ofinefficiency may involve current that bypasses the cell pairs by flowingthrough the dilute and concentrate inlet and outlet manifolds. Openinlet and outlet manifolds may be in direct fluid communication withflow compartments and may reduce pressure drop in each flow path. Partof the electrical current from one electrode to the other may bypass thestack of cell pairs by flowing through the open areas. The bypasscurrent reduces current efficiency and increases energy consumption.Another potential source of inefficiency may involve ions that enter thedilute stream from the concentrate due to imperfect permselectivity ofion exchange membranes. In some embodiments, techniques associated withthe sealing and potting of membranes and screens within a device mayfacilitate reduction of current leakage.

In one or more embodiments, a bypass path through a stack may bemanipulated to promote current flow along a direct path through a cellstack so as to improve current efficiency. In some embodiments, anelectrochemical separation device may be constructed and arranged suchthat one or more bypass paths are more tortuous than a direct paththrough the cell stack. In at least certain embodiments, anelectrochemical separation device may be constructed and arranged suchthat one or more bypass paths present higher resistance than a directpath through the cell stack. In some embodiments involving a modularsystem, individual modular units may be configured to promote currentefficiency. Modular units may be constructed and arranged to provide acurrent bypass path that will contribute to current efficiency. Innon-limiting embodiments, a modular unit may include a manifold systemand/or a flow distribution system configured to promote currentefficiency. In at least some embodiments, a frame surrounding a cellstack in an electrochemical separation modular unit may be constructedand arranged to provide a predetermined current bypass path. In someembodiments, promoting a multi-pass flow configuration within anelectrochemical separation device may facilitate reduction of currentleakage. In at least some non-limiting embodiments, blocking membranesor spacers may be inserted between modular units to direct dilute and/orconcentrate streams into multiple-pass flow configurations for improvedcurrent efficiency. In some embodiments, current efficiency of at leastabout 60% may be achieved. In other embodiments, a current efficiency ofat least about 70% may be achieved. In still other embodiments, acurrent efficiency of at least about 80% may be achieved. In at leastsome embodiments, a current efficiency of at least about 85% may beachieved.

In accordance with one or more embodiments, a method for preparing acell stack for an electrical purification apparatus may comprise formingcompartments. A first compartment may be formed by securing ion exchangemembranes to one another to provide a first spacer assembly having afirst spacer disposed between the ion exchange membranes. For example, afirst cation exchange membrane may be secured to a first anion exchangemembrane at a first portion of a periphery of the first cation exchangemembrane and the first anion exchange membrane to provide a first spacerassembly having a first spacer disposed between the first cationexchange membrane and the first anion exchange membrane.

A second compartment may be formed by securing ion exchange membranes toone another to provide a second spacer assembly having a second spacerdisposed between the ion exchange membranes. For example, a second anionexchange membrane may be secured to a second cation exchange membrane ata first portion of a periphery of the second cation exchange membraneand the second anion exchange membrane to provide a second spacerassembly having a second spacer disposed between the second anionexchange membrane and the second cation exchange membrane.

A third compartment may be formed between the first compartment and thesecond compartment by securing the first spacer assembly to the secondspacer assembly, and by positioning a spacer therebetween. For example,the first spacer assembly may be secured to the second spacer assemblyat a second portion of the periphery of the first cation exchangemembrane and at a portion of the periphery of the second anion exchangemembrane to provide a stack assembly having a spacer disposed betweenthe first spacer assembly and the second spacer assembly.

Each of the first compartment and the second compartment may beconstructed and arranged to provide a direction of fluid flow that isdifferent from the direction of fluid flow in the third compartment. Forexample, the fluid flow in the third compartment may be running in adirection of a 0° axis. The fluid flow in the first compartment may berunning at 30°, and the fluid flow in the second compartment may berunning at the same angle as the first compartment) (30° or at anotherangle, such as 120°. The method may further comprise securing theassembled cell stack within a housing.

In accordance with one or more embodiments, an electrochemicalseparation system may include a cross-flow design. A cross-flow designmay allow for increased membrane utilization, lower pressure drop and areduction in external leaks. Additionally, limitations on operatingpressure may be reduced by a cross-flow design. In at least someembodiments, the pressure rating of a shell and endcaps may be the onlysubstantial limitations on operating pressure. Automation ofmanufacturing processes may also be achieved.

In accordance with one or more embodiments, a first fluid flow path anda second fluid flow path may be selected and provided by way of theportions of the peripheries of the ion exchange membranes that aresecured to one another. Using the first fluid flow path as a directionrunning along a 0° axis, the second fluid flow path may run in adirection of any angle greater than zero degrees and less than 360°. Incertain embodiments of the disclosure, the second fluid flow path mayrun at a 90° angle, or perpendicular to the first fluid flow path. Inother embodiments, the second fluid flow path may run at a 180° angle tothe first fluid flow path. If additional ion exchange membranes aresecured to the cell stack to provide additional compartments, the fluidflow paths in these additional compartments may be the same or differentfrom the first fluid flow path and the second fluid flow path. Incertain embodiments, the fluid flow path in each of the compartmentsalternates between a first fluid flow path and a second fluid flow path.For example, the first fluid flow path in the first compartment may berunning in a direction of 0°. The second fluid flow path in the secondcompartment may be running in a direction of 90°, and the third fluidflow path in the third compartment may be running in a direction of 0°.In certain examples, this may be referred to as cross-flow electricalpurification.

In other embodiments, the fluid flow path in each of the compartmentsalternates sequentially between a first fluid flow path, a second fluidflow path, and a third fluid flow path. For example, the first fluidflow path in the first compartment may be running in a direction of 0°.The second fluid flow path in the second compartment may be running at30°, and the third fluid flow path in the third compartment may berunning at 90°. The fourth fluid flow path in the fourth compartment maybe running at 0°. In another embodiment, the first fluid flow path inthe first compartment may be running in a direction of 0°. The secondfluid flow path in the second compartment may be running at 60°, and thethird fluid flow path in the third compartment may be running at 120°.The fourth fluid flow path in the fourth compartment may be running at0°. In some embodiments, one or more flow paths may be substantiallynon-radial. In at least some embodiments, one or more flow paths mayfacilitate achieving a substantially uniform liquid flow velocityprofile within the system.

In accordance with one or more embodiments, the flow within acompartment may be adjusted, redistributed, or redirected to providegreater contact of the fluid with the membrane surfaces within thecompartment. The compartment may be constructed and arranged toredistribute fluid flow within the compartment. The compartment may haveobstructions, projections, protrusions, flanges, or baffles that mayprovide a structure to redistribute the flow through the compartment,which will be discussed further below. In certain embodiments, theobstructions, projections, protrusions flanges, or baffles may bereferred to as a flow redistributor. A flow redistributor may be presentin one or more of the compartments of the cell stack.

Each of the compartments in the cell stack for an electricalpurification apparatus may be constructed and arranged to provide apredetermined percentage of surface area or membrane utilization forfluid contact. It has been found that greater membrane utilizationprovides greater efficiencies in the operation of the electricalpurification apparatus. Advantages of achieving greater membraneutilization may include lower energy consumption, smaller footprint ofthe apparatus, less passes through the apparatus, and higher qualityproduct water. In certain embodiments, the membrane utilization that maybe achieved is greater than 65%. In other embodiments, the membraneutilization that may be achieved is greater than 75%. In certain otherembodiments, the membrane utilization that may be achieved may begreater than 85%. The membrane utilization may be at least in partdependent on the methods used to secure each of the membranes to oneanother, and the design of the spacer. In order to obtain apredetermined membrane utilization, appropriate securing techniques andcomponents may be selected in order to achieve a reliable and secureseal that allows optimal operation of the electrical purificationapparatus, without encountering leakage within the apparatus. In someembodiments, stack production processes may involve thermal bondingtechniques to maximize membrane utilization, while maintaining a largesurface area of membrane that may be used in the process.

In accordance with one or more embodiments, an electrical purificationapparatus comprising a cell stack is provided. The electricalpurification apparatus may comprise a first compartment comprising ionexchange membranes and may be constructed and arranged to provide adirect fluid flow in a first direction between the ion exchangemembranes. The electrical purification apparatus may also comprise asecond compartment comprising ion exchange membranes and may beconstructed and arranged to provide a direct fluid flow in a seconddirection. Each of the first compartment and the second compartment maybe constructed and arranged to provide a predetermined percentage ofsurface area or membrane utilization for fluid contact.

An electrical purification apparatus may comprise a cell stack. Theelectrical purification apparatus may comprise a first compartmentcomprising a first cation exchange membrane and a first anion exchangemembrane, the first compartment constructed and arranged to provide adirect fluid flow in a first direction between the first cation exchangemembrane and the first anion exchange membrane. The apparatus may alsocomprise a second compartment comprising the first anion exchangemembrane and a second cation exchange membrane to provide a direct fluidflow in a second direction between the first anion exchange membrane andthe second cation exchange membrane. Each of the first compartment andthe second compartment may be constructed and arranged to provide apredetermined membrane utilization, for example, a fluid contact ofgreater than 85% of the surface area of the first cation exchangemembrane, the first anion exchange membrane and the second cationexchange membrane. At least one of the first compartment and the secondcompartment may comprise a spacer, which may be a blocking spacer.

In accordance with one or more embodiments, the electrical purificationapparatus comprising a cell stack may further comprise a housingenclosing the cell stack, with at least a portion of a periphery of thecell stack secured to the housing. A frame may be positioned between thehousing and the cell stack to provide a first modular unit in thehousing. A flow redistributor may be present in one or more of thecompartments of the cell stack. At least one of the compartments may beconstructed and arranged to provide flow reversal within thecompartment.

In some embodiments of the disclosure, a cell stack for an electricalpurification apparatus is provided. The cell stack may provide aplurality of alternating ion depleting and ion concentratingcompartments. Each of the ion depleting compartments may have an inletand an outlet that provides a dilute fluid flow in a first direction.Each of the ion concentrating compartments may have an inlet and anoutlet that provides a concentrated fluid flow in a second directionthat is different from the first direction. A spacer may be positionedin the cell stack. The spacer may provide structure to and define thecompartments and, in certain examples, may assist in directing fluidflow through the compartment. The spacer may be a blocking spacer whichmay be constructed and arrange to redirect at least one of fluid flowand electrical current through the cell stack. As discussed, theblocking spacer may reduce or prevent electrical current inefficienciesin the electrical purification apparatus.

In some embodiments of the disclosure, an electrical purificationapparatus is provided. The apparatus may comprise a cell stackcomprising alternating ion diluting compartments and ion concentratingcompartments. Each of the ion diluting compartments may be constructedand arranged to provide a fluid flow in a first direction. Each of theion concentrating compartments may be constructed and arranged toprovide a fluid flow in a second direction that is different from thefirst direction. The electrical purification apparatus may also comprisea first electrode adjacent an anion exchange membrane at a first end ofthe cell stack, and a second electrode adjacent a cathode exchangemembrane at a second end of the cell stack. The apparatus may furthercomprise a blocking spacer positioned in the cell stack and constructedand arranged to redirect at least one of a dilute fluid flow and aconcentrate fluid flow through the electrical purification apparatus andto prevent a direct current path between the first electrode and thesecond electrode. As discussed above, the blocking spacer may beconstructed and arranged to reduce electrical current inefficiencies inthe electrical purification apparatus.

The cell stack for the electrical purification apparatus may be enclosedin a housing with at least a portion of a periphery of the cell stacksecured to the housing. A frame may be positioned between the housingand the cell stack to provide first modular unit in the housing. Asecond modular unit may also be secured within the housing. A blockingspacer may also be positioned between the first modular unit and thesecond modular unit. A flow redistributor may be present in one or moreof the compartments of the cell stack. At least one of the compartmentsmay be constructed and arranged to provide flow reversal within thecompartment. A bracket assembly may be positioned between the frame andthe housing to provide support to the modular unit and to secure themodular unit within the housing.

The fluid flow in the first direction may be a diluting stream and thefluid flow in the second direction may be a concentrating stream. Incertain embodiments, the fluid flow in the first direction may beconverted to a concentrating stream and the fluid flow in the seconddirection may be converted to a diluting stream with the use of polarityreversal where the applied electrical field is reversed thus reversingthe stream function. Multiple spacer assemblies separated by spacers maybe secured together to form a stack of cell pairs, or a membrane cellstack.

The electrical purification apparatus of the present disclosure mayfurther comprise a housing that encloses the cell stack. At least aportion of the periphery of the cell stack may be secured to thehousing. A frame or support structure may be positioned between thehousing and the cell stack to provide additional support to the cellstack. The frame may also comprise inlet manifolds and outlet manifoldsthat allow the flow of liquid in and out of the cell stack. The frameand the cell stack together may provide an electrical purificationapparatus modular unit. The electrical purification apparatus mayfurther comprise a second modular unit secured within the housing. Aspacer, for example, a blocking spacer, may be positioned between thefirst modular unit and the second modular unit. A first electrode may bepositioned at an end of the first modular unit that is opposite an endin communication with the second modular unit. A second electrode may bepositioned at an end of the second modular unit that is opposite an endin communication with the first modular unit.

A bracket assembly may be positioned between the frame and the housingof the first modular unit, the second modular unit, or both. The bracketassembly may provide support to the modular units, and provide for asecure attachment to the housing. In one embodiment of the disclosure,the electrical purification apparatus may be assembled by positioning amembrane cell stack into a housing or vessel. Endplates may be providedat each end of the cell stack. Adhesive may be applied to seal at leasta portion of the periphery of the cell stack to the inside wall of thehousing.

In certain embodiments of the disclosure, an electrical purificationapparatus is provided that reduces or prevents inefficiencies resultingfrom greater electrical power consumption. The electrical purificationapparatus of the present disclosure may provide for a multiple pass flowconfiguration to reduce or prevent current inefficiencies. The multiplepass flow configuration may reduce the bypass of current through theflow manifolds, or leakage of current, by eliminating or reducing thedirect current path between the anode and the cathode of the electricalpurification apparatus. In certain embodiments of the disclosure theflow within a compartment may be adjusted, redistributed, or redirectedto provide greater contact of the fluid with the membrane surfaceswithin the compartment. The compartment may be constructed and arrangedto redistribute fluid flow within the compartment. The compartment mayhave obstructions, projections, protrusions, flanges, or baffles thatmay provide a structure to redistribute the flow through thecompartment. The obstructions, projections, protrusions, flanges, orbaffles may be formed as part of ion exchange membranes, the spacer, ormay be an additional separate structure that is provided within thecompartment. In at least one embodiment, a membrane or blocking spacermay be substantially non-conductive so as to impact current flow withinthe system.

In some embodiments of the present disclosure, a method is provided forsecuring or bonding ion exchange membranes and, optionally, spacers toproduce a membrane cell stack for an electrical purification apparatus.The method may provide for securing of multiple anion exchange membranesand cation exchange membranes for use in electrical purificationapparatus such as a cross-flow electrodialysis (ED) modular unit.

In certain embodiments of the disclosure, a method of preparing a firstcell stack for an electrical purification apparatus is provided. Themethod may comprise securing a first ion exchange membrane to a secondion exchange membrane. A spacer may be positioned between the first ionexchange membrane and the second ion exchange membrane to form a spacerassembly. When used in an electrical purification apparatus, this spacerassembly defines a first compartment that may allow fluid flow. Aplurality of ion exchange membranes may be secured to one another toprovide a series of compartments. In certain embodiments, a plurality ofspacer assemblies may be constructed and the spacer assemblies may besecured to one another. A spacer may be positioned between each of thespacer assemblies. In this way, a series of compartments for anelectrical purification apparatus is constructed to allow fluid flow inone or more directions in each of the compartments.

The spacers that may be positioned within the compartments may providestructure to and define the compartments and, in certain examples, mayassist in directing fluid flow through the compartment. The spacers maybe made of polymeric materials or other materials that allow for adesired structure and fluid flow within the compartments. In certainembodiments, the spacers may be constructed and arranged to redirect orredistribute fluid flow within the compartments. In some examples, thespacer may comprise a mesh-like or screen material to provide structureand allow for the desired fluid flow through the compartment. The spacermay be constructed and arranged to redirect at least one of fluid flowand electrical current to improve process efficiency. The spacer mayalso be constructed and arranged to create multiple fluid flow stages inan electrical purification apparatus. The spacer may comprise a solidportion to redirect fluid flow in a particular direction. The solidportion may also redirect electrical current flow in a particulardirection, and prevent a direct path between an anode and a cathode inan electrical purification apparatus. In some embodiments, a spacer maypromote current flow through a cell stack and generally deter currentbypass with respect to the cell stack. A spacer comprising a solidportion may be referred to as a blocking spacer. The blocking spacer maybe positioned within a cell stack, or may be positioned between a firstcell stack, or first modular unit, and a second cell stack, or secondmodular unit.

In some embodiments, the plurality of ion exchange membranes secured toone another may alternate between cation exchange membranes and anionexchange membranes to provide a series of ion diluting compartments andion concentrating compartments. The geometry of the membranes may be ofany suitable geometry such that the membranes may be secured within acell stack. In certain embodiments, a particular number of corners orvertices on the cell stack may be desired so as to suitably secure thecell stack within a housing. In certain embodiments, particularmembranes may have different geometries than other membranes in the cellstack. The geometries of the membranes may be selected to assist in atleast one of securing the membranes to one another, to secure spacerswithin the cell stack, to secure membranes within a modular unit ormodular unit, to secure membranes within a support structure, to securea group of membranes such as a cell stack to a housing, and to secure amodular unit or modular unit into a housing. The membranes, spacers, andspacer assemblies may be secured at a portion of a periphery or edge ofthe membranes, spacers, or spacer assemblies. A portion of a peripherymay be a continuous or non-continuous length of the membrane, spacer, orspacer assembly. The portion of the periphery that is selected to securethe membrane, spacer, or spacer assembly may provide a boundary orborder to direct fluid flow in a predetermined direction.

In accordance with one or more embodiments, a cell stack as discussedherein may have any desired number of ion exchange membranes, cell pairsor flow compartments. In some embodiments, an electrochemical separationsystem may include a single cell stack. In other embodiments, such as inmodular embodiments, and electrochemical separation system may includetwo or more cell stacks. In some embodiments, each cell stack may beincluded in a separate modular unit as discussed herein. Modularity mayoffer design flexibility and ease of manufacturability.

In accordance with one or more embodiments, an electrochemicalseparation system may include a first electrode, a second electrode, afirst electrochemical separation modular unit having a first cell stackdefining a plurality of alternating depleting compartments andconcentrating compartments supported by a first frame, the firstelectrochemical separation modular unit positioned between the firstelectrode and the second electrode, and a second electrochemicalseparation modular unit, in cooperation with the first electrochemicalseparation modular unit, having a second cell stack defining a pluralityof alternating depleting compartments and concentrating compartmentssupported by a second frame, the second electrochemical separationmodular unit positioned between the first electrochemical separationmodular unit and the second electrode. The first cell stack may besurrounded by the first frame, and the second cell stack may besurrounded by the second frame. In some embodiments, the first andsecond electrochemical separation modular units are arranged fluidly inparallel. The first and second electrochemical separation modular unitsmay each be of unitary construction or may themselves be constructed ofsub-blocks. The first and second electrochemical separation modularunits may be removable. In some embodiments, a blocking spacer may bepositioned between the first and second electrochemical separationmodular units. As discussed below, each of the frames may include amanifold system and/or a flow distributions system. The first and secondelectrochemical separation modular units may be mounted in a vessel,such as with a bracket assembly. The system may include two, three, fouror more modular units depending on an intended application and variousdesign elements. A source of water to be treated may be fluidlyconnected to an inlet of the vessel. The depleting compartments andconcentrating compartments may each have an inlet in fluid communicationwith the inlet of the vessel.

In some non-limiting embodiments, at least one of the depletingcompartments and concentrating compartments comprises a flowredistributor. In some embodiments, the system is configured such that adirection of flow through the depleting compartments is different than adirection of flow through the concentrating compartments. In at leastone embodiment, the system may be configured such that the direction offlow through the depleting compartment is substantially perpendicular tothe direction of flow through the concentrating compartments. The firstand second electrochemical separation modular units may be configured tofacilitate multi-pass flow within the system.

In accordance with one or more embodiments, a method of assembling aseparation system may include mounting a first electrochemicalseparation modular unit having a first cell stack surrounded by a firstframe in a vessel between a first electrode and a second electrode, andmounting a second electrochemical separation modular unit having asecond cell stack surrounded by a second frame in the vessel between thefirst electrochemical separation modular unit and the second electrode.The method may further comprise disposing a blocking spacer between thefirst and second electrochemical separation modular units. Theperformance of each of the first and second electrochemical separationmodular units may be tested prior to mounting in the vessel. A source ofwater to be treated may be fluidly connected to an inlet of the vessel.

In accordance with one or more embodiments, one, two or more modularunits may be inserted between a first electrode and a second electrode.In some embodiments, two modular units may be substantially adjacent oneanother within the system. In other embodiments, a blocking spacer maybe positioned between two adjacent modular units. In at least certainembodiments, a modular unit in a separation system may not have adedicated set of electrodes. Instead, multiple modular units may bepositioned between a single pair of electrodes.

In accordance with one or more embodiments, an electrochemicalseparation modular unit may comprise a cell stack defining a pluralityof alternating depleting compartments and concentrating compartments,and a support system. The support system may be configured to maintainvertical alignment of the cell stack. The support system may be a framein some embodiments. A frame may at least partially surround the cellstack. In other embodiments, the frame may substantially surround thecell stack. In some embodiments, a frame may include a manifold systemconfigured to facilitate fluid flow through the cell stack. A manifoldsystem may deliver process liquid from a central system manifold to anindividual modular unit that it services. A manifold system may includean inlet manifold and an outlet manifold. A manifold system may comprisean inlet manifold in fluid communication with an inlet of each depletingcompartment and with an inlet of each concentrating compartment. Themanifold system may further comprise an outlet manifold in fluidcommunication with an outlet of each depleting compartment and with anoutlet of each concentrating compartment. The manifold system may beconfigured to deliver treated liquid downstream via the outlet manifold.At least a portion of the manifold system may be integral to the frameor in a structure separate from the frame. In at least some embodiments,the manifold system may be constructed and arranged to prevent mixing ofdilute and concentrate streams in a modular unit. The manifold systemmay fluidly isolate and keep separated outlets of dilute and concentratecompartments associated with a stack.

In some embodiments, a support system such as a frame may include a flowdistribution system. The flow distribution system may be a part of themanifold system or a separate system. The flow distribution system maybe in fluid communication with the manifold system and may be configuredto promote uniform flow distribution to a cell stack. The flowdistribution system may be in fluid communication with an inlet of eachdepleting compartment and with an inlet of each concentratingcompartment. In some embodiments, at least a portion of the flowdistribution system may be integral to the frame. In other embodiments,at least a portion of the flow distribution system may engage with theframe. In some embodiments, at least a portion of the flow distributionsystem comprises an insert that is removably receivable by the frame.This may be for ease of manufacturability of one or more features of theflow distribution system. One or more features of the manifold and/orflow distribution system may be integrated into the frame such as via aninsert structure. In some embodiments, a flow distribution system mayengage with each inlet and outlet of the cell stack. In someembodiments, a frame may include an insert associated with at least oneside of the cell stack. In at least some embodiments, a frame mayinclude an insert associated with each side of the cell stack. Forexample, a rectangular cell stack may include four inserts. The manifoldsystem and/or flow distribution system or component thereof may beassociated with each side of a cell stack.

In accordance with one or more embodiments, a flow distribution systemor an insert associated with a modular unit frame may be constructed andarranged to supply liquid to be treated to inlets of dilute andconcentrate compartments of a cell stack. The flow distribution systemor insert may be further constructed and arranged to receive and fluidlyisolate outlet streams associated with dilute and concentratecompartments of the cell stack. The flow distribution system or insertmay keep dilute and concentrate outlet streams separated. Variousdesigns for flow distributions systems capable of having the intendedfunctionality may be implemented in accordance with one or moreembodiments. Based on the nature of the cell stack, compartment inletsand outlets may be positioned on one or more sides of the cell stack. Insome embodiments, compartment inlets and outlets may be positioned onall sides of the cell stack. The design of the frame, including manifoldsystem and flow distribution systems, may be configured such that it mayreceive the cell stack in any orientation. Inserts or flow distributorsmay also be inserted into any side of the frame and be associated withany side of the cell stack for flexibility. An insert or flowdistributor may be inserted and serve to both provide fluid to betreated to the multiple compartment of the stack, as well as fluidlyisolate and keep separate outlet streams of the cell stack. Further asdiscussed herein, the insert or flow distributor may also be constructedand arranged to improve current efficiency of the overall modular unit.

In one or more embodiments, a bypass path through a stack may bemanipulated to promote current flow along a direct path through a cellstack so as to improve current efficiency. In some embodiments, anelectrochemical separation device may be constructed and arranged suchthat one or more bypass paths are more tortuous than a direct paththrough the cell stack. In at least certain embodiments, anelectrochemical separation device may be constructed and arranged suchthat one or more bypass paths present higher resistance than a directpath through the cell stack. In some embodiments involving a modularsystem, individual modular units may be configured to promote currentefficiency. Modular units may be constructed and arranged to provide acurrent bypass path that will contribute to current efficiency. Innon-limiting embodiments, a modular unit may include a manifold systemand/or a flow distribution system configured to promote currentefficiency. In at least some embodiments, a frame surrounding a cellstack in an electrochemical separation modular unit may be constructedand arranged to provide a predetermined current bypass path. In someembodiments, inserts associated with the support system, such ascomponents of a manifold or flow distribution system, may be configuredto promote current efficiency.

In accordance with one or more embodiments, at least one of the manifoldsystem and the flow distribution system may be constructed and arrangedto improve efficiency of a modular unit. The flow distribution systemmay comprise at least one bypass path configured to reduce current loss.The flow distribution system may include a plurality of first fluidpassages oriented in a first direction. The flow distribution system mayfurther comprise a plurality of second fluid passages oriented in asecond direction and in fluid communication with the plurality of firstfluid passages. In some embodiments, the first and second directions maybe substantially perpendicular. The flow distribution system maycomprise an insert, wherein the frame defines a recess configured toreceive the insert. The insert may define a lattice structure configuredto promote uniform flow distribution to the cell stack in at least someembodiments.

In some non-limiting embodiments, the insert may have a first sideproximate the cell stack, and a second side opposite the first side. Theinsert may comprise a plurality of ports on at least one of the firstand second sides. In some embodiments, at least some of the ports may beslots or grooves. Ports may be different on one side of the insertversus another side. In some embodiments, each port on the first side ofthe insert may be oriented substantially perpendicular to ion exchangemembranes of the cell stack, and each port on the second side of theinsert may be oriented substantially parallel to ion exchange membranesof the cell stack. In some embodiments, at least one port on the firstside is in fluid communication with two or more compartments of the cellstack. A plurality of ports may be staggered on a side of the insert. Aport may service one or multiple compartments. A cell stack may beconstructed and arranged to achieve at least about 85% fluid contactwith respect to surface area of ion exchange membranes defining the cellstack in some embodiments. At least one of the depleting compartmentsand concentrating compartments may include a blocking spacer or flowredistributor. In some embodiments, a cell stack is configured such thata direction of flow through the depleting compartments is different thana direction of flow through the concentrating compartments. In at leastone embodiment, the cell stack is configured such that the direction offlow through the depleting compartment is substantially perpendicular tothe direction of flow through the concentrating compartments.

In accordance with one or more embodiments, an electrochemicalseparation modular unit may include a flow distributor configured topromote uniform flow distribution within a cell stack. The flowdistributor may be integral to the structure of a frame or manifoldsurrounding the cell stack. In other embodiments, at least a portion ofthe flow distributor may be configured to engage with the frame ormanifold. The flow distributor may comprise an insert removablyreceivable by the frame. The modular unit can include one or more flowdistributors. In some embodiments, a flow distributor may be associatedwith one or more sides of the cell stack. In at least some embodiments,a flow distributor may be associated with each side of the cell stack.Each side of the cell stack may have a dedicated flow distributor. Aflow distributor may be configured to be removably received by theelectrochemical separation device. Multiple-pass flow configuration maybe possible with use of blocking membranes.

In accordance with one or more embodiments, a flow distributor forelectrochemical separation may include a plurality of first passagesoriented in a first direction and configured to deliver feed to at leastone compartment of an electrochemical separation device, and a pluralityof second passages oriented in a second direction, the plurality ofsecond passages in fluid communication with the plurality of firstpassages and with an inlet manifold associated with the electrochemicalseparation device. In some embodiments, the first direction issubstantially vertical. In at least one embodiment, the second directionis substantially horizontal. The plurality of first passages may bearranged in parallel. In at least one embodiment, the plurality ofsecond passages may be arranged in parallel. In some embodiments, atleast one first passage intersects at least one second passage. Ablocking member may be positioned at an intersection of a first passageand a second passage. The plurality of first passages and the pluralityof second passages may be arranged to reduce current leakage within theelectrochemical separation device. The plurality of first passages maybe arranged with the plurality of second passages to define a latticestructure in some non-limiting embodiments.

In accordance with one or more embodiments, a flow distributor may havea first side configured to be disposed proximate a cell stack of theelectrochemical separation device. The distributor may include aplurality of ports on the first side. The flow distributor of claim mayhave a second side arranged opposite the first side and may have aplurality of ports on the second side. The plurality of ports on thefirst and second sides may comprise slots or grooves in someembodiments. In at least one embodiment, the ports may be different onthe first and second side. Each port on the first side may be orientedsubstantially perpendicular to compartments of the electrochemicalseparation device in some non-limiting embodiments. Each port on thesecond side may be oriented substantially parallel to compartments ofthe electrochemical separation device. The plurality of ports on thesecond side may be configured to distribute fluid flow to the pluralityof ports on the first side. In some embodiments, at least one port onthe first side may be in fluid communication with two or morecompartments of electrochemical separation device. In some embodiments,the plurality of ports on the first side or the second side may bestaggered. The flow distributor may be constructed and arranged topromote current flow to operating surfaces of the electrochemicalseparation device. A port may be associated with the flow distributor.The port may have various positions with respect to the flowdistributor. The flow distributor may comprise a port substantiallycentered with respect to the flow distributor to promote uniform flowdistribution from the inlet manifold to the compartments of theelectrochemical separation device. In other embodiments, a port may beoffset relative to the flow distributor.

In accordance with one or more embodiments, a stack of cell pairs may beconstructed to form a modular unit or sub-block for quality controlprior to final assembly into an electrochemical separation system. Thesub-blocks may be formed by thermal bonding, adhesive or other method.In some embodiments, a cross-flow modular unit may be assembled after asub-block of cell pairs is tested. Ports may be embedded on walls of acasing to allow for multiple dumping during operation. In a cross-flowmodular unit there may be a large number of cell pairs stacked andpacked in a shell or housing. Seals may be associated with the cellpairs to define flow paths. If even one of the seals fails then theentire modular unit may be deemed inoperable. In accordance with one ormore embodiments, sub-blocks of cell pairs may be used to detectdefective seals before stacking all of the cell pairs to form a largermodular unit or system. In some embodiments, cell pairs may be brokendown into stacks each packaged in a frame to determine seal integrityprior to final assembly. In some embodiments, the packaging method mayuse an O-ring or a gasket to mechanically connect a sub-block to eitheranother sub-block or an electrode-plate without any internal cross-leakor external leakage. Frame design may facilitate multi-dumps ofconcentrate fluid such that a standard sub-block may be manufactured,stocked, and easily configured into any desired number of passes anddumps per modular unit for a specific operating condition. Frame designmay promote uniform flow distribution, isolation of dilute andconcentrate streams, as well as current efficiency

In accordance with one or more embodiments, a frame may tightly supportsides of a stack of cell pairs to maintain alignment. Vertical slots mayconnect inlet and outlet manifolds to the flow compartments. This maypromote uniform flow distribution across a width of flow compartmentsand reduce current leakage from compartments to manifolds. Membranes atthe ends of a stack may be secured and sealed to the frame with o-ringsor other mechanism. A frame may be assembled from multiple sections ormay be integral, such as molded as one part. Each modular unit mayfunction as a one pass with a blocking membrane sealed in betweenmodular units. Modular units next to endblocks may be separated fromelectrode compartments by membranes and may also be sealed, such as witho-ring or adhesive. A modular unit frame, or the manifold system of amodular unit frame, may generally include one or more dilute ports andone or more concentrate ports. The ports may be on the frame or on aninsert. The modular unit frame may also include a flow distributionsystem that may include one or more inserts or flow distributorsremovably receivable by the frame. The frame may include one or morerecesses sized and shaped to receive an insert. The overall frame andmodular unit design may be configured to reduce bypass current. A bypasspath may be tortuous and present higher resistance than a direct paththrough the stack. In some non-limiting embodiments, current may onlybypass the stack by flowing through the bottom half of slots, along thehorizontal manifolds to the port manifold, back along the top horizontalmanifold and back into the stack through the top half of slots.

In accordance with one or more specific non-limiting embodiments, astack 110 of cell pairs may be enclosed on four sides in a frame 120 ofunitary construction to form modular unit 100, as shown in FIG. 1. FIGS.2 and 3 present views through Section A-A. The thicknesses of the flowcompartments and the membranes are exaggerated for clarity. A set ofmanifolds in the frame section supplies the feed to the inlet of thedilute compartments via an array of slots oriented perpendicularly tothe membrane surfaces. At the outlet of the dilute compartments, productwater flows through a second array of slots and enters a second set ofmanifolds in the frame section at the right of the figure. A sectionperpendicular to Section A-A would show the same arrangement ofmanifolds and slots for the concentrate compartments.

The inlet and outlet to the dilute and concentrate compartments may beisolated from each other by seals between the corners of the stack andthe frame as shown in FIG. 2. The seals can be achieved by varioustechniques such as adhesives, thermal bonds or combinations thereof.FIG. 4 shows one method of sealing the corners. The stack 410 isinserted into the frame 420 and a potting adhesive is dispensed into thegap between the stack 410 and the frame 420 to form modular unit 400.After the adhesive has set, the stack and frame are rotated 90° and thenext corner is potted, and so on. Further curing at an elevatedtemperature may be necessary to fully develop the properties of theadhesive. Alternatively a molten hot melt adhesive of low enoughviscosity can be dispensed into the gaps until all four corners arepotted.

The frame of the overall design described above may serve severalfunctions. It may maintain alignment of the cell pairs in the stack.Energy consumption in an ED device can be reduced by decreasing thethickness of the flow compartments and the membranes. Flow compartments(inter-membrane distance) in a current state of the art device can be asthin as 0.38 mm (0.015″) while membrane thickness can be as low as 30microns (0.0012″). A stack of 1200 cell pairs, assembled from such thinand flexible components has very little rigidity and should be supportedfrom lateral shifting. This problem is particularly acute in atraditional plate-and-frame device which requires compression to sealthe components of the stack and relies on side support channels andtie-bars to align the stack. The problem is still present in across-flow device, even though the stack components are sealed eitherwith adhesives or thermal bonding and the entire stack is housed in acylindrical vessel. The slots that connect the inlet and outletmanifolds to the flow compartments, when properly designed, can ensurethat flow is uniformly distributed across the inlet of each dilutecompartment. The slots are oriented perpendicular to the flowcompartments. There is no need to line up the slots with the inlets ofindividual compartments. The slots reduce the area available for currentleakage from the stack into the inlet and outlet manifolds and therebythe fraction of current which bypasses the stack of membranes and cell.Current bypass reduces current efficiency (theoretical currentrequired/actual current measured, based on Faraday's constant of 96,498coulombs/equivalent) and increases energy consumption per unit volume ofproduct. Other methods to improve current efficiency involve the use ofmulti-pass modular unit configurations using blocking membranes orspacers.

In another embodiment, the configuration of the slots can be modified tofurther reduce current leakage and thus improve the current efficiencywith the placement of blocks within the slots. FIG. 5 shows modular unit500 including a stack 510 of cell pairs in a frame 520 with inlet andoutlet ports oriented vertically. FIG. 6 is a section view showing theflow path for Stream 1. From the inlet port, the fluid flows into theflow compartments in the stack via three horizontal inlet manifolds inparallel followed by vertical slots. From the stack, the fluid flows tothe outlet port though another set of vertical slots and three outletmanifolds.

FIG. 7 shows that the current, however, can potentially bypass the stack710 by flowing through the vertical slots from one end of the stack tothe other. FIG. 8 shows one non-limiting embodiment of the slotmodification with reference to modular unit 800. Obstacles orobstructions may be placed in the slots to force the bypass current totake a more circuitous path and thereby increase the electricalresistance in the bypass paths. In some embodiments, blocks, such ashorizontal blocks may be placed in the slots.

In some embodiments, the horizontal blocks are not in the same locationsin every slot; otherwise one or more flow compartments may be completelyblocked off from the inlet or outlet manifolds. FIG. 9 shows how theblocks 930 can be staggered so only a small fraction of the inlet oroutlet to any given flow compartment would be blocked. Uniform averageflow velocity in the compartment can still be achieved by proper designof the inter-membrane screen. In some embodiments, the staggered blocksmay all line up with one of the horizontal manifolds if the frame is tobe machined or molded in one piece, which restricts the number andlocations of the blocks.

In another embodiment, the frame is machined or molded without theslots. Grids which contain the slots and horizontal blocks arefabricated separately and inserted into the frame 1020 as flowdistributor 1050 shown in FIGS. 10 and 11. There is then moreflexibility in the number and locations of blocks. The blocks can bearranged in arrays or at random.

The frame can be fabricated from materials with the requisite mechanicalproperties and chemical compatibility with the fluid to be deionized byED. In applications such as desalination of seawater, for example,plastic materials are favored because of their resistance to corrosionand low cost. Potential plastics include polyvinyl chloride (PVC),polyethylene (PE), polypropylene (PP), polyamides (PA or nylon),acrylonitrile butadiene styrene (ABS), polysulfone or blends of plasticssuch as Noryl, which is a blend of polyphenylene oxide (PPO) andpolystyrene (PS). Reinforcing fillers such as glass fibers may be addedfor enhancement of chemical resistance and mechanical and thermalproperties.

In some embodiments, the frame can be fabricated using methods such asmachining and/or injection molding. In addition, “rapid prototyping”techniques such as stereolithography, 3D printing, fused depositionmodeling, etc. can be used for fabrication of the frame. In anotherembodiment, the frame 1220 is assembled from four sections joined byadhesives, thermal or mechanical methods, or combinations thereof, asshown in FIG. 12. The sections can be fabricated using the samematerials and methods as described above.

The frame can be as deep as necessary to accommodate the number of cellpairs in a stack (see height “D” in FIG. 2), particularly if the frameis assembled from sections. To accommodate a stack of 1200 cell pairs,for example, with 0.38 mm (0.015″) inter-membrane distance and 30 micron(0.0012″) thick membranes, the depth the frame would have to be about0.984 m (38.74″).

There may be practical limitations, however, on manufacturing of such anassembly. Insertion of a stack with a large number of cell pairs into adeep frame may be difficult. The flexible membranes and screens in thestack are initially connected only by adhesive or thermal seals, so thestack has no rigidity. Potting the corners may become more difficult asthe height of the stack increases. A potting adhesive, for example,needs to be dispensed uniformly along the entire length of the gapbetween the stack and the frame as shown in FIG. 4. The seals in a stackassembled in a frame may not be tested until the corners are potted. Theentire assembly may have to be rejected if any of the seals fail,resulting in complete loss of materials and labor.

FIG. 13 is a schematic, for example, of the dilute stream in a 3-pass EDdevice with 1200 cell pairs. There are 6 modular units, each with 200cell pairs. Alternatively, 3 modular units may be used, each with 400cell pairs. Many combinations of cell pairs and number of passes arepossible. Additionally, the configuration can be asymmetric withdifferent numbers of cell pairs in each pass. This invention is notlimited to any specific number of cell pairs or number of passes.

FIG. 14 shows a modular unit 1400 as another embodiment. FIGS. 15 and 16are views through Section A-A and B-B, respectively. The thicknesses ofthe flow compartments and the membranes are again greatly exaggeratedfor clarity. Each compartment is filled with a screen that separates theadjacent membranes and enhances mixing of the fluid as it flows throughthe compartment. FIG. 15 is a view through Section A-A in FIG. 14,showing flow through the dilute compartments. The last membrane at thetop of the stack (AEM) and the last membrane at the bottom (CEM) extendbeyond the stack and are sealed by O-rings secured by clips. Thesemembranes isolate the dilute stream (inlet and outlet manifolds, slotsand compartments) from the last concentrate compartments at the top andbottom ends of the stack. FIG. 16 presents a close up view of the inletto the dilute compartments. FIG. 17 is a view through Section B-B ofFIG. 14. The concentrate stream flows through all of the concentratecompartments in parallel, including the one at the top and bottom endsof the stack.

The outer O-ring on the top surface of the frame of FIG. 15 is used toseal the modular unit against an adjacent flat surface, which can be thetop plate of a test device, the frame of an adjacent modular unit above,or an endplate. FIG. 18 shows, for example, a section view through amodular unit device 1800 to test the integrity of the seals in a modularunit. The modular unit is clamped between two plates. The bottom platehas an O-ring which seals against the bottom surface of the modular unitframe. The O-ring at the top of the modular unit seals against the topplate. The dilute outlet port is plugged and a pressurized fluid or gasis applied to the dilute inlet port. A leak in any of bonds between themembranes or at any corner seal will result in a cross-leak to theconcentrate stream The presence or rate of cross-leak can be used as acriteria for determining modular unit quality. FIG. 19 shows a stack ofendplates, modular units 1900 and separating membranes 1970 beforeassembly. The components can be aligned using locating pins, forexample.

In some embodiments, each modular unit may use the same frame design.The frame for Unit 2 may be oriented perpendicularly to the frames forUnits 1 and 3 as illustrated by the locations of the clips. The stacksinside Units 1 and 3 are the same, but different from the stack insideUnit 2. FIG. 20 is a view through Section A-A in Unit 1 and FIG. 21 is aview through Section B-B in Unit 2. The last compartments at the top andbottom of Unit 1 are concentrate compartments, the last membrane at thetop is an extended or separating AEM and the last membrane at the bottomis an extended or separating CEM. In Unit 2, the last compartments atthe top and bottom are dilute compartments, the last membrane at the topis an extended CEM and the last membrane at the bottom is an extended orseparating AEM.

The arrangement of membranes and cells in the modular units, along withblocking membranes, as shown in the schematic in FIG. 22, allowsmulti-pass flow configurations in the dilute and concentrate streams andresults in concentrate compartments next to the electrode compartments.Those concentrate compartments serve as buffer cells between theelectrode compartments and the next dilute. FIG. 23 is a view through anassembled ED device showing the 3-pass flow through the dilutecompartments. FIG. 24 is a detailed view of the dilute outlet of ModularUnit 1 and dilute inlet of Unit 2 illustrating blocking spacer 2470between modular units 2400.

A section view through the assembled ED modular unit perpendicular tothe section in FIG. 23 would show the 3-pass flow through theconcentrate compartments. The endplates in the ED device shown in FIG.19 and FIG. 23 can be drawn together using threaded rods with nuts atthe ends, commonly called tie-rods or tie-bars in plate-and-frame EDdevices. The endplates must apply sufficient compression to the modularunits to seal the O-rings. Other apparatus can also be used to applycompressive force to the modular units. One example would a pressurizedbladder located at the end of the stack of modular units. The tie-barscan be arranged outside the frame (outboard), or the walls of the framescan be thick enough to allow the tie-bars to be located inside the walls(inboard). The ED device can be enclosed for cosmetic or safety reasons.The enclosure can be assembled from thermo-formed plastic panels, forexample. The ED device can also be inserted into a pressure vessel forsafety and structural reasons. In some embodiments, the frames aresquare in external shape and have walls that are essentially solid. Thewalls may be cored out if the frames are to be injection molded to avoidexcessively thick sections. Pressurized fluid is pumped through themodular units during operation, so reinforcing ribs may be added to thewall for stiffness and strength. The external shape of the frames neednot be square. For example, FIG. 25 shows a frame 2520 that issubstantially circular in external shape and designed for injectionmolding. Rectangles, hexagons and octagons are among other possibleshapes. The sides of the frame also can be asymmetrical in length andnumber.

FIG. 26 shows six modular units 2600 between two molded endplates, allhoused in a cylindrical vessel 2680 (shown transparent). O-rings on theendplates seal against the inside wall of the cylinder at the ends. Thecylinder can have multiple functions, including alignment of modularblocks during assembly, structural support to the round frames as theflow compartments and manifolds inside the ED device are pressurizedduring operation, prevention of external leaks if any of the O-ringsbetween the modular units and between the units and the endplates wereto leak, and as a cosmetic cover. The cylindrical vessel may not benecessary if the frames can be designed and fabricated with sufficientstiffness and strength. One or more non-structural cosmetic covers canbe used to enclose the modular units. FIGS. 27 and 28 each illustrate amodular unit inserted into a circular enclosure without a frame. FIGS.29 and 30 illustrate a modular unit constructed with a frame 3020containing slots 3090.

This invention is not limited in use to electrodialysis equipment. Otherelectrochemical deionization device such as electrodeionization (EDI) orcontinuous electrodeionization (CEDI) can also be constructed using across flow configuration with multiple passes using a modular frame withslots in which cell pairs are inserted.

In cross-flow electrodialysis (ED) and electrodeionization (EDI) devicesthe diluting and concentrating streams flow in directions perpendicularto each other. Potential applications include desalination of seawater,brackish water and brines from oil and gas production.

Various designs and manufacturing methods may be used cross-flow modularunits. In some non-limiting embodiments, modular units may beincorporated into a vessel. In at least one non-limiting embodiment, thevessel may be substantially cylindrical. FIG. 27 illustrates a 50 cellpair modular unit. In this design, open inlet and outlet manifolds arein direct fluid communication with the flow compartments as illustratedin FIG. 28. The open manifolds reduce pressure drop in each stream, butpart of the electrical current from one electrode to the other canbypass the stack of cell pairs by flowing through the open areas. Thebypass current reduces current efficiency and increases energyconsumption. For desalination of NaCl solutions, current efficiency maybe calculated as follows:

$\eta_{i} = \frac{\left\lbrack {{\left( q_{d} \right)_{in}C_{in}} - {\left( q_{d} \right)_{out}C_{out}}} \right\rbrack {zF}}{I}$

where:

η_(i)=current efficiency

(q_(d))_(in)=flow rate per dilute compartment at inlet

(q_(d))_(out)=flow rate per dilute compartment at inlet

C_(in)=concentration at dilute inlet

C_(out)=concentration at dilute outlet

z=valence=1 for NaCl

F=Faraday's constant

I=current

For desalination of seawater, current efficiency may be calculated asfollows:

$\eta_{i} = \frac{\left\lbrack {{\left( q_{d} \right)_{in}\left( {\sum\limits_{i}{C_{i}z_{i}}} \right)_{in}} - {\left( q_{d} \right)_{out}\left( {\sum\limits_{i}{C_{i}z_{i}}} \right)_{out}}} \right\rbrack F}{I}$

where:

C_(i)=concentration of individual ions

z_(i)=valence of individual ions

A “process efficiency η_(p)” may be defined as follows for NaClsolutions:

$\eta_{p} = \frac{\left( q_{d} \right)_{out}\left( {C_{in} - C_{out}} \right)z\; F}{I}$

The process efficiency is generally less than or equal to the currentefficiency:

$\eta_{p} = {\eta_{i} - \frac{{\Delta \left( q_{d} \right)}C_{in}{zF}}{I}}$

where:

Δ(q_(d))=rate of water loss from the dilute compartment due toelectro-osmosis or osmosis.

In some embodiments, systems and methods may support a stack of cellpairs on all sides by a frame. The frame may have vertical slots whichconnect the inlet and outlet manifolds for the dilute and concentratestreams to their respective flow compartments in the stack asillustrated in FIGS. 29 and 30. Among the expected benefits of such adesign is reduction of current bypass by elimination of the open areasat the inlets and outlets to the stack. A stack of cell pairs can bepotted at the corners in a frame to form a modular sub-block that can bechecked for cross-leaks, desalination performance and pressure drop.Multiple blocks can be stacked to form an ED modular unit. Blockingmembranes can be inserted between the blocks to direct the dilute and/orconcentrate stream into multiple-pass flow configurations. FIG. 31illustrates transport processes in an ideal electrochemical separationsystem. FIG. 32 illustrates transport processes involving currentinefficiencies within an electrochemical separation system and FIG. 33illustrates transport processes involving current inefficiency incombination with water loss an electrochemical separation system.

FIG. 34 illustrates that the current can still bypass the stack byflowing through the gaps between the frame and the stack and within thevertical slots from one end of the stack to the other. Current bypassthrough the slots is therefore significant. In accordance with one ormore embodiments, methods may reduce current bypass in cross-flow EDdevices. In some embodiments, flow passages in a sub-block frame mayreduce the fraction of current that bypasses the stack and therebyincrease current efficiency. The passages may connect the inlet andoutlet ports to the flow compartments in the stack of cell pairs. FIG.35 shows the fluid volume in flow passages inside a sub-block frame.Stream 1, for example, enters the frame at an inlet port and flowsthrough a lattice of passages into the stack. For simplicity the fluidvolume in the stack is represented by a transparent block. The actualfluid volume in the flow compartments in the stack is defined by themembranes and the screens. From the stack Stream 1 flows to the outletport via a second lattice of passages. Stream 2 is orientedperpendicular to Stream 1; otherwise the design of flow passages is thesame.

FIG. 36 is a detailed view of the inlet flow passages for Stream 1. Flowfrom the inlet port is distributed to a number of horizontal passages inparallel. Each horizontal passage in turn distributes its portion of theflow to a number of flow compartments in the stack via verticalpassages. At the outlet of the flow compartments, the reverse sequenceof passages (vertical passages→horizontal passages→outlet port) allowsthe flow to exit the sub-block.

FIG. 37 shows that the bypass current can flow from one end of the stackto the other only through a series of vertical and horizontal passages;the horizontal passages are in fluid communication with each other onlythrough the port manifolds. There are two sets of bypass paths, one viathe inlet port manifold and the other via the outlet port manifold.Insert 3795 includes inlet manifold 3797.

The current paths through the sub-block can therefore be represented asa circuit with three resistors in parallel; one is the resistance of thecell pairs in the stack and the other two are resistances of the twosets of paths for the bypass current.

By proper sizing of the passages, the electrical resistance of theconvoluted paths for the bypass current can be made significantly higherthan the resistance of the direct path through the stack. The majorityof the current can therefore be forced to flow through the stack. In atleast some embodiments, at least 70% of the current may flow through thestack and therefore at least about 70% current efficiency may beachieved. In at least some embodiments, at least 80% of the current mayflow through the stack and therefore at least about 80% currentefficiency may be achieved. In at least some embodiments, at least 90%of the current may flow through the stack and therefore at least about90% current efficiency may be achieved.

The flow passages adjacent to the stack are oriented vertically so thateach communicates with several cell pairs. They are staggered verticallyas shown in FIG. 38 so that every flow compartment is in communicationwith multiple vertical passages. The dimensions and spacing of thevertical and horizontal flow passages affect the flow distribution inthe flow compartment in the stack and the overall pressure drop in thetwo streams. Computational Fluid Dynamics (CFD) software can be used tooptimize the design.

In some embodiments, the internal flow passages as shown in FIG. 36 maybe formed in a block of material. Thus, the internal flow passages maybe integral to the frame. In other embodiments, at least a portion ofthe flow passages may be formed in a separate section of material andthen inserted into the frame. For example, an insert may include aportion of the flow passages. An insert may include slots and/or groovesthat are fabricated separately and then installed in a frame.

FIG. 39 shows the vertical slots on one face of an insert 3995 and thehorizontal grooves on the other to form respectively the vertical andhorizontal flow passages. The insert can be fabricated by machining orby molding. FIG. 40 shows an example of a frame 4020 design amenable tofabrication by machining. The frame has four recesses 4025 for insertsand four relatively wide grooves to form the port manifolds. Featuressuch as grooves for O-rings to seal a sub-block to another are not shownfor clarity. FIG. 41 shows a section view through the frame with aninsert 4095 about to be installed. All four inserts, two for eachstream, are installed before the stack is potted to the frame withadhesives at the corners. FIG. 42 is a section view that shows how eachhorizontal passage is in fluid communication with a number of verticalpassages in parallel and how the horizontal passages are in fluidcommunication with each other via the port manifold. The stack of cellpairs is again represented by a transparent box for simplicity. Theinsert as shown also has additional slots on the top and bottom that arein fluid communication with slots in the frame that supply flow to thetop and bottom ends of the stack. FIG. 43 shows an example of a moldedframe 4310 that can accommodate the inserts shown in FIG. 39. The framedesign can be optimized using Finite Element Analysis (FEA) software tominimize weight, which affect part cost, while meeting mechanicalspecifications on deflection and stress under a maximum internalpressure. FIG. 44 shows another example of a molded frame 4420. Therecesses 4425 for the inserts have curved walls that conform to theoverall circular shape of the frame. Multiple sub-blocks using thisframe design can be stacked up and inserted into a cylindrical housing.FIG. 45 shows a corresponding insert with the horizontal grooves on thecurved side. Not all of the flow passages have to be placed in theinserts. Horizontal grooves can be located in the frames 4620 to providethe horizontal flow passages while the vertical slots can be located inthe inserts as illustrated in FIG. 46. Selection of the best frame andinsert design for a cross-flow modular unit will be affected by therelative complexity and costs of component fabrication and assembly.

The insert and frames may be fabricated from materials with therequisite mechanical properties and chemical compatibility with thefluid to be treated. In applications such as desalination of seawater,for example, plastic materials are favored because of their resistanceto corrosion and low cost. Potential plastics include polyvinyl chloride(PVC), polyethylene (PE), polypropylene (PP), polyamides (PA or nylon),acrylonitrile butadiene styrene (ABS), polysulfone or blends of plasticssuch as Noryl, which is a blend of polyphenylene oxide (PPO) andpolystyrene (PS). Reinforcing fillers such as glass fibers may be addedfor enhancement of chemical resistance and mechanical and thermalproperties.

In accordance with one or more embodiments, an electrochemicaldeionization device may comprise at least one cell pair and a frame. Theat least one cell pair may be contained within the frame. In someembodiments, the electrochemical deionization device may comprise anelectrodialysis device. In other embodiments, the electrochemicaldeionization device may comprise an electrodeionization device. Theframe may include one or more slots. In some embodiments, blocks may bewithin the slots. In at least one embodiment, the slots may beperpendicular to the at least one cell pair.

In accordance with one or more embodiments, a cross-flow electrochemicalseparation device may comprise a modular unit. The modular unit maycomprise at least one cell pair and a frame. The at least one cell pairmay be attached to the frame. The device may be an electrodialysisdevice. In other embodiments, the device may be an electrodeionizationdevice. The frame may include one or more slots. In some embodiments,blocks may be within the slots. In at least one embodiment, the slotsmay be perpendicular to the at least one cell pair. The device mayfurther include a blocking membrane or spacer between each modular unit.The device may include a plurality of modular units. The modular unitsmay be arranged to allow a multi-pass flow configuration. In someembodiments, the modular units may be contained within a cylindricalvessel.

In accordance with one or more embodiments, a method of assembly of anelectrochemical deionization device may include bonding a first ionexchange membrane to a first screen, bonding a second ion exchangemembrane to the first ion exchange membrane and screen, bonding a secondscreen to the first ion exchange membrane, first screen and second ionexchange membrane to form a cell pair, bonding a plurality of cell pairstogether to form a stack of cell pairs, inserting the stack of cellpairs into a frame, and sealing the stack of cell pairs to the frame toform a modular unit. The method may further involve sealing a first ionexchange membrane to a first side of the modular unit, and sealing asecond ion exchange membrane to a second side of the modular unit. Insome embodiments, the method may further include placing a first modularunit on a second modular unit, placing an additional modular unit on thefirst and second modular units, and repeating to obtain a plurality ofmodular units of a desired number. The plurality of modular units may beinserted into a cylindrical vessel.

In some non-limiting embodiments, a stack of cell pairs may start andend with extended membranes. This may help isolate dilute, concentrateand electrode streams within a frame. The extended membranes may be of adifferent shape than the remainder of the membranes in the stack. Theextended membranes may be bonded to the main stack on at least one side,such as on two sides. In some embodiments, corners of screen mayprotrude out of the stack at membrane corners. Protruding corners ofscreen may later act as a reinforcement to secure the membranes aftercorner potting or may wick to draw low-viscosity potting material intothe stack during corner potting. An extended portion of top and bottommembranes may be folded as shown in FIG. 47A and bonded as shown in FIG.47B to form a compartment after completing the potting of four corners.With the compartment formed, the integrity of the seals in the stack maybe checked. An opening may then be created to allow dilute fluid to bediverted into another sub-block after final assembly. Concentrate may beseparated from dilute and electrode fluid. O-rings or gaskets may beused where a sub-block is joined to another sub-block or to an electrodeplate. In some embodiments, a single o-ring or gasket may be used toform a connection. In a sub-block, four pieces of inner supportingstructure may be potted together with four corners of the stack tocreate a flat surface on a side wall for inlet and outlet ports. Portsmay be important during assembly of two sub-assemblies as they providean alternate flow path to separate concentrate and dilute stream at asub-block connection to ensure streams will not mix. They may alsocreate flat and solid surfaces on the membrane above and below it tofacilitate sealing between sub blocks and end blocks during assembly. Anexternal supporting structure may act as reinforcement to withholdpositive pressure of the modular unit, preventing membrane rupture. Itmay also work with the inner supporting structure to strengthen bonding.Protrusions on each piece of external supporting structure may provideguidance during assembly to prevent misalignment. Port connectors mayprovide connection of sub-blocks. It may be plugged when flow pathacross sub block connection through extended membrane is required. Thismay also clamp the external and inner supporting structure in positionto ensure that all four sides of the extended membrane are folded into aframe-like pattern before injecting a potting material to mold thecorners. The top and bottom screen may be potted together with thecorners potting to provide additional holding strength to the extendedmembranes. The two screens may serve as a spacer between the extendedmembranes of the sub-blocks at each connection. Grooves for o-ring orgaskets may be molded into both ends of the corners potted profile.During operation the corners potted profile may hold inner and externalsupporting structure together to withstand positive pressure in themanifolds. The potted corner portion that wicks through the corners ofthe screen may act to seal the stack. It may also serve as an isolatingblock to separate the dilute manifold from the concentrate manifoldpreventing cross-leak. The ends of the corner profile may act as astopper preventing over clamp down of the sealing at all connections.FIG. 47C illustrates an assembly in accordance with these embodiments.In some embodiments, manufacturing may involve a first set of bondingbetween membranes and a second set of bonding at four-corners of astack. Multiple modular units may be assembled, such as with o-rings,and sub-block quality control testing may be conducted duringproduction.

In accordance with one or more embodiments, a cell stack may be securedwithin a frame or support structure comprising an inlet manifold and anoutlet manifold to provide a modular unit or modular unit. This modularunit may then be secured within a housing. The modular unit may furthercomprise a bracket assembly or corner support that may secure themodular unit to the housing. A second modular unit may be secured withinthe housing. One or more additional modular units may also be securedwithin the housing. In certain embodiments of the disclosure, a blockingspacer may be positioned between the first modular unit and the secondmodular unit. In some non-limiting embodiments, stacks of cell pairswith dilute and concentrate compartments in single-pass flowconfigurations may be sealed in sections to form modular units. Theunits may be joined together with blocking spacers in between to formmultiple pass configurations. The stacks may be sealed to the housingsection using adhesive at corners. The blocking spacers do not have tobe sealed to the inside wall of the housing but are instead sandwichedbetween modular units and sealed between the ends. In some non-limitingembodiments, two modular units with flanges at ends may be stacked witha blocking spacer in between. The flanges may be bolted together. Theblocking spacer may be molded with a frame and sealed between theflanges with adhesives or gaskets. Alternatively, the frame may bemolded of a thermoplastic material or other fabrication method. In someembodiments, modular units may be connected with clamps or tie bars. Thedesign of the blocking spacer may be modified accordingly. FIG. 48illustrates one non-limiting embodiments of modular units assembled witha flange.

In accordance with one or more embodiments, an insert as discussedherein may be designed to promote even flow distribution and with lowerpressure drop across a membrane in a flow through an electrochemicalseparation device. Even flow distribution may help prevent scaling inspacers and improve current efficiency. Inlet and outlet port locationand an insert's opening size may be varied to impact flow distribution.CFD software may facilitate evaluation of flow distribution and pressuredrop. Lower pressure drop may lead to a lower pumping requirement.Modular unit cost may also be reduced as the modular unit may be builtwith thinner material. Inserts may act as a flow distributor and improvecurrent efficiency. The size of ports or sots may be varied on theinsert to vary flow distribution. FIG. 49 illustrates a flow distributoror insert 4995 with ports 4997 located towards center. In someembodiments, the size of slots on the insert may be varied at differentlocations.

The function and advantages of these and other embodiments will be morefully understood from the following examples. The examples are intendedto be illustrative in nature and are not to be considered as limitingthe scope of the embodiments discussed herein.

Example 1

Two modular units were constructed using a cross-flow configuration.Both modular units contained 50 cell pairs in a single pass. The controlmodular unit did not include a frame but was simply inserted into acircular enclosure as illustrated in FIGS. 27 and 28. The second modularunit was constructed with a frame containing slots as illustrated inFIGS. 29 and 30. The effective area per membrane for both modular unitsis 0.024 m2. The flow path length is 17.1 cm. The intermembrane spacingis 0.038 cm. Both modular units were operated on a feed water containingNaCl. An electric potential was applied to both modular units and thecurrent efficiency determined.

The operating parameters were as follows:

Modular unit Control Frame Feed Conductivity mS/cm 56.16 55.9 ProductConductivity 55.23 54.08 mS/cm Amperage A 2.01 3.0 Product Flow Ratel/min 2.81 2.66 Current Efficiency % 49 63.3

The control modular unit without the frame had a measured currentefficiency of 49%. The modular unit with the frame had a measuredcurrent efficiency of 63.3%. This represents approximately a 29%improvement in current efficiency when using a frame with slots.

Example 2

A prototype modular unit with 145 cell pairs in a 3-pass flowconfiguration was assembled. The cell pairs were in 3 frames, containing50 cell pairs, 50 cell pairs and 45 cell pairs, respectively. In testswith 56 mS/cm NaCl solution as feed, the average process efficiency was65% with flow velocity in the range of 2.0-4.3 cm/s.

Example 3

A modular unit with an insert in the supporting frame (Beta 2.5) wasoperated in comparison to a modular unit without an insert in thesupporting frame (Beta 2). The data is presented in FIG. 4, illustratinga higher pressure drop associated with the insert.

Example 4

A modular unit with an insert having a central manifold was modeled andsimulated using computational fluid dynamics (CFD) software incomparison to a modular unit with an insert having an offset manifold.The results indicated that the offset manifold was associated with awider region of low velocity flow at the sides than the centralmanifold. Scaling may be more likely to form at regions of low velocityso the central manifold may provide better flow distribution. Thecentral manifold was also associated with a pressure drop about 14%lower than that of the offset manifold.

It is to be appreciated that embodiments of the methods and apparatusesdiscussed herein are not limited in application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the accompanying drawings. Themethods and apparatuses are capable of implementation in otherembodiments and of being practiced or of being carried out in variousways. Examples of specific implementations are provided herein forillustrative purposes only and are not intended to be limiting. Inparticular, acts, elements and features discussed in connection with anyone or more embodiments are not intended to be excluded from a similarrole in any other embodiment.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. Any references toembodiments or elements or acts of the systems and methods hereinreferred to in the singular may also embrace embodiments including aplurality of these elements, and any references in plural to anyembodiment or element or act herein may also embrace embodimentsincluding only a single element. The use herein of “including,”“comprising,” “having,” “containing,” “involving,” and variationsthereof is meant to encompass the items listed thereafter andequivalents thereof as well as additional items. References to “or” maybe construed as inclusive so that any terms described using “or” mayindicate any of a single, more than one, and all of the described terms.Any references to front and back, left and right, top and bottom, upperand lower, and vertical and horizontal are intended for convenience ofdescription, not to limit the present systems and methods or theircomponents to any one positional or spatial orientation.

Having described above several aspects of at least one embodiment, it isto be appreciated various alterations, modifications, and improvementswill readily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be part of thisdisclosure and are intended to be within the scope of the invention.Accordingly, the foregoing description and drawings are by way ofexample only.

What is claimed is:
 1. An electrochemical separation system, comprising: a first electrode; a second electrode; a first electrochemical separation modular unit including a plurality of alternating depleting compartments and concentrating compartments positioned between the first and second electrodes; and a second electrochemical separation modular unit including a plurality of alternating depleting compartments and concentrating compartments, the second electrochemical separation modular unit arranged in cooperation with the first electrochemical separation modular unit and positioned between the first electrochemical separation modular unit and the second electrode; wherein each of the first and second electrochemical separation modular units includes a cell stack defining the plurality of alternating depleting compartments and concentrating compartments, and a support system configured to maintain vertical alignment of the cell stack, the support system comprising a frame surrounding the cell stack, and wherein the frame includes a manifold system and a flow distribution system in fluid communication with the manifold system, the flow distribution system comprising at least one bypass path configured to reduce current loss within the system.
 2. The system of claim 1, wherein the spacer is configured to promote current flow to the depleting and concentrating compartments within the system. 3-7. (canceled)
 8. The system of claim 1, wherein the first and second electrochemical separation modular units are arranged in parallel.
 9. The system of claim 1, wherein the first and second electrochemical separation modular units are removable.
 10. The system of claim 9, wherein the first and second electrochemical separation modular units are mounted in a vessel.
 11. The system of claim 10, further comprising a source of water to be treated fluidly connected to an inlet of the vessel.
 12. The system of claim 11, wherein the plurality of depleting compartments and concentrating compartments each has an inlet in fluid communication with the inlet of the vessel.
 13. The system of claim 1, wherein the flow distribution system comprises an insert, and wherein the frame defines a recess configured to receive the insert.
 14. The system of claim 13, wherein the insert defines a lattice structure configured to promote uniform flow distribution to the cell stack.
 15. The system of claim 1, wherein the first and second electrochemical separation modular units are configured to provide non-radial flow within the system.
 16. The system of claim 1, wherein the first and second electrochemical separation modular units are configured to provide a uniform liquid flow velocity profile within the system.
 17. The system of claim 1, wherein the system is constructed and arranged to achieve at least about 85% fluid contact with respect to surface area of ion exchange membranes defining the electrochemical separation modular units.
 18. The system of claim 1, wherein at least one of the depleting compartments and concentrating compartments comprises a blocking spacer or a flow redistributor.
 19. The system of claim 1, wherein the system is configured such that a direction of flow through the depleting compartments is different than a direction of flow through the concentrating compartments.
 20. The system of claim 1, wherein the system is configured such that the direction of flow through the depleting compartment is substantially perpendicular to the direction of flow through the concentrating compartments.
 21. An electrochemical separation system, comprising: a first electrode; a second electrode; a first electrochemical separation modular unit including a cell stack defining a plurality of alternating depleting compartments and concentrating compartments positioned between the first and second electrodes, and a frame surrounding the cell stack, the frame having a manifold system and a flow distribution system in fluid communication with the manifold system, the flow distribution system comprising at least one bypass path configured to reduce current loss within the electrochemical separation system; and a second electrochemical separation modular unit including a cell stack defining a plurality of alternating depleting compartments and concentrating compartments, and a frame surrounding the cell stack, the frame having a manifold system and a flow distribution system in fluid communication with the manifold system, the flow distribution system comprising at least one bypass path configured to reduce current loss within the electrochemical separation system, the second electrochemical separation modular unit arranged in cooperation with the first electrochemical separation modular unit and positioned between the first electrochemical separation modular unit and the second electrode.
 22. The system of claim 21, wherein the system is constructed and arranged to achieve at least about 85% fluid contact with respect to surface area of ion exchange membranes defining the electrochemical separation modular units.
 23. The system of claim 21, wherein at least one of the depleting compartments and concentrating compartments comprises a blocking spacer or a flow redistributor.
 24. The system of claim 21, wherein the system is configured such that the direction of flow through the depleting compartment is substantially perpendicular to the direction of flow through the concentrating compartments.
 25. The system of claim 21, wherein each flow distribution system comprises an insert, and wherein each frame defines a recess configured to receive the insert. 